In previous engines exhaust gas recirculation (EGR) systems may be employed to reduced emissions. The EGR systems typically route exhaust gas from an exhaust conduit to an intake conduit in the engine. Some EGR systems also employ EGR coolers designed to remove heat from the EGR gas to enable a greater mass of EGR gas to be introduced into the intake system, to further reduce emissions.
However, EGR systems may be shut-down during certain periods of engine operation, such as during start-up (e.g., cold start). Consequently, the EGR cooler may remain unused during these periods of EGR inactivity. However, it may be desirable to extract heat from exhaust gas during such time periods. Thus, previous EGR systems may not efficiently operate the EGR cooler during certain operating conditions, thereby decreasing the system's efficiency.
Against the background of that stated above and recognizing the aforementioned problems the inventors have developed a method for operating an internal combustion engine. The method includes closing an EGR valve positioned in an exhaust gas recirculation (EGR) conduit downstream of an EGR cooler, the EGR conduit coupled to an intake system and an exhaust system and determining a profile of exhaust pressure waves in the exhaust system. The method also includes adjusting a volume of variable volume vessel based on the profile of the exhaust pressure waves, the variable volume vessel positioned downstream of the EGR cooler and upstream of the EGR valve. Consequently, pressure waves in the exhaust system can be leveraged to enable EGR cooler operation during periods of EGR inactivity. The energy extracted by the EGR cooler may be used to heat engine coolant and/or engine oil, for example, to increase combustion efficiency and correspondingly reduce emissions.
Specifically, in one example, the volume of the variable volume vessel may be adjusted to reinforce pressure wave propagation through the EGR cooler while the EGR valve is closed. In this manner, the variable volume vessel enables the acoustics in the EGR system to be tuned to promote and reinforce wave propagation therethrough. Consequently, the EGR cooler can extract heat from exhaust gas while the EGR valve is closed, thereby increasing engine efficiency.
It should be understood that the summary above is provided to introduce in simplified form a selection of concepts that are further described in the detailed description. It is not meant to identify key or essential features of the claimed subject matter, the scope of which is defined uniquely by the claims that follow the detailed description. Furthermore, the claimed subject matter is not limited to implementations that solve any disadvantages noted above or in any part of this disclosure.